Issue 5/2005
09/02/05
New rope load measuring principle saves calibration and reduces rope wear
The Henning rope load measuring system WeightWatcher embodies a new measurement principle: At each rope, an individual load sensor is mounted which no longer has to be calibrated at the lift using weights, but can be optionally used in any location. The measurement signals are collated in an indicator unit, permitting a check of both the cab weight and even rope tension.
Category: Issue 5/2005
Posted by: Editor
The Henning rope load measuring system WeightWatcher embodies a new measurement principle: At each rope, an individual load sensor is mounted which no longer has to be calibrated at the lift using weights, but can be optionally used in any location. The measurement signals are collated in an indicator unit, permitting a check of both the cab weight and even rope tension.
It is only by providing an evenly distributed load between the individual ropes of the set that it is possible to ensure even rope wear and prolong service life. When installing and in running operation, uneven loads can be exerted due to production tolerances in terms of the rope diameter, groove diameter or taper angle, imprecise setting of the rope tensioner or different degrees of friction (lubrication). The negative results range from exacerbated wear of the ropes subjected to higher loads through to the dreaded “sawing effect” in the rope groove. If these faults are discovered at an early stage, targeted corrective action can be taken on the ropes or traction sheave before premature damage has a chance to occur.
The special feature of the new sensor is the USB port integrated in the indicator unit. This permits the rope setting to be performed on a computer-aided basis in just a few minutes. Every rope only has to be “handled” once, i.e. set to a calculated target value. Thanks to an intelligent evaluation algorithm, an optimum rope setting result is achieved immediately.
The indicator unit features three alarm outputs which can operate optionally as NC or NO contacts. The alarm thresholds can be freely programmed (e.g. no load, full payload, overload). A fourth output emits an alarm in the event of rope slack situations or indicates critical error statuses in the individual rope tension levels.
Approach and braking processes can be optimized by linking the indicator to frequency converters using optional analogue measurement signal output or an optional CANOpen interface.
The measurement principle when using load sensors tensioned in the rope is based on the deflection of the rope from its extended length and measurement of the restoring force. All previous load measuring systems which were attached directly in the suspension rope (Fig. 4) have to be laboriously calibrated using weights at the lift installation by means of half load compensation, as both the rope diameter (d) and the influences from rope flexure, rope rigidity and rope structure falsify the measurement result.
The patented design of the new Henning load sensor (Fig. 5) compensates for these influences, meaning that laborious calibration using weights at the lift installation itself is no longer required. As a result, the new sensor is equally suitable for different rope diameters and types and can be put to immediate use. In order to eliminate the influencing factors described above, in the Henning load sensor the rope is deflected by two clamping elements K1 and K2 which absorb all unwanted forces and transmit only the restoring force in the form of tilting moment MB to the sensor (cf. Fig. 5).
The LS1 load sensor is based on this new measurement principle. Fig. 1 illustrates the design for fixed, permanent installation at the lift. An independently operating system is also currently under development which will permit individual rope loads as well as cab and counter weights to also be measured on a mobile basis. In conjunction with the Henning acceleration sensor used for mobile diagnosis, this will allow the effectiveness of the stopping brake to be precisely measured under no-load conditions, including the influence of the counterweight. On this basis, the effectiveness of the stopping brake under full load conditions can be precisely calculated and recorded without the need to transport weights to the site.
A summary of benefits afforded by the new rope load sensor:
• New measurement principle enhances measurement accuracy without elaborate calibration work (weights)
• Suitable for use with different rope diameters and types
• Determination of different rope tension levels
• Rope tension compensation in a single work cycle
• Prolonged rope life due to even rope tension
• In-process monitoring of rope tension
• Slack rope alarm
• Simple installation
• Complies with all load measurement requirements for traction lifts
• Output of measurement data via USB port, CANOpen (optional) and DC signal (optional)
Tim Ebeling, Henning GmbH, Schwelm
Peter Pini, Ingenieurbüro IPP, Braunschweig
Peter Pini, Ingenieurbüro IPP, Braunschweig
Henning GmbH, D-58332 Schwelm
5/2005
